Asimple gut operation that sees a plastic film inserted into the stomach could cure or control diabetes, British doctors have found.

Patients taking part in trials at King’s College Hospital and University College Hospital in London and City Hospital in Birmingham found their diabetes had disappeared or become much milder after the operations.

Francesco Rubino, professor of metabolic surgery at King’s, told The Sunday Times: “About 50 per cent of patients are diabetes-free after these procedures.

The increased number of people with diabetes has been linked to rising levels of obesity

“The remaining people demonstrate big improvements of blood sugar control and can drastically reduce their dependence on insulin or other medication.

“In many patients, blood sugar levels go back to normal within days, long before declines in fat levels or weight.”

The treatments stem from a new view of the causes of diabetes, a condition in which there is too much glucose in the blood.

Diabetes has previously been blamed on the pancreas not secreting enough insulin, the hormone that controls glucose levels – but Rubino and his colleagues believe the gut is the key player.

Andrea Midmer, 59, a nurse, took part in the trial, in which a plastic liner or “endobarrier” was fitted into her stomach to stop the walls of her upper gut coming into contact with the food she ate.

“The effect was immediate,” said Midmer, who weighed 20 stone and was on insulin when the trial started. I stopped feeling hungry, I ate much smaller meals and I lost 4½ stone.”

Type 2 diabetes, which is often linked to obesity, is one of Britain’s biggest health problems and affects about four million people.

Treatment costs £10 billion a year – about 10 per cent of the NHS budget. That figure is expected to rise to 17 per cent if the numbers suffering from the condition his five million, as is predicted, by 2025.

The increased number of people with the disease has been linked to rising levels of obesity.

Between 1993 and 2010 the proportion of obese people in the UK went from 13 per cent to 26 per cent for men and from 16 per cent to 26 per cent for women.